Been trying to use the same mpv build I use with SMPlayer for Syncplay.
For example, my mpv executable is located in "C:\Program Files\SMPlayer\mpv\mpv.exe".
This is detected as mplayer, so trying to use it results in an "Fatal Error" message.
Putting a copy of mpv elsewhere or renaming the directory to not contain "mplayer" works of course, but it would be nice if that wasn't necessary.